1. Field of the Invention
The present invention relates to an exposure mask fabrication method, an exposure mask fabrication system, and a semiconductor device fabrication method. More specifically, the present invention relates to, for example, an apparatus and method for writing a pattern onto a mask substrate with electron beams in order to fabricate a mask to be used for an EUV (Extreme Ultra Violet) exposure.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 16 is a conceptual diagram explaining operations of a variable shaping type electron beam writing or “drawing” apparatus. The variable shaping electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during the writing. In other words, a quadrangular shape that can pass through both the aperture 411 and the variable shape aperture 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
With recent miniaturization of semiconductor devices, further shortening the wavelength itself of exposure light is considered. Regarding developing new microlithography technique, light of 157 nm has been given up due to lack of lens material used for image reducing or transferring. For this reason, extreme ultraviolet (EUV) light with a wavelength of 13.4 nm is thought to be the most promising at present. Since the EUV light, whose wavelength is classified into the soft X-ray region, is transmitted and/or absorbed by many materials, it cannot form a projection optical system any longer. Therefore, a catoptric system is proposed for the exposure method using the EUV light. Thus, in the EUV lithography, a catoptric system composed of a multilayer mirror (mirror of multilayer film) which reflects EUV light is used. An EUV exposure mask intervenes as a part of the optical system. Therefore, a reflection-type mask wherein a multilayer film is formed on the substrate is employed. The multilayer film formed by alternately layering molybdenum (Mo) and silicon (Si) is used.
Then, if the regularity of each layer thickness of these laminated layers breaks down, the phase of reflected light will be shifted. As a result, a phase defect will be exposed on the wafer. Thus, it is desirable that there is no defect on the surface of the multilayer substrate. Moreover, it is desirable to prevent particulate contamination which may generate a defect from being included in the multilayer film. Furthermore, since the EUV mask is a part of the catoptric system, irregularity of the mask surface will generate a shift of the phase of reflected light on the reflection surface. Consequently, there will be generated a positional deviation or size irregularity of a pattern to be transferred or printed onto a wafer at the time of exposure. Due to the reason described above, the substrate itself is required to have highly precise flatness.
However, it is difficult to completely reduce the defect rate of a substrate to zero, and if selecting only a substrate that has no defect or satisfies specification after inspecting all fabricated masks, it will make the substrate very expensive.
Then, in order to avoid transferring or printing a defect of a mask in exposure processing, there is disclosed a technique in which a phase defect on a multilayer mask is prevented from being transferred or printed because, by shifting a pattern, the phase defect is included in the region of an absorber pattern (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2001-033941).
It is necessary to previously specify the position of a defect by an inspection apparatus which inspects particulate contamination of a mask blank (substrate), and to reflect the specified position to pattern data such that the pattern layout is shifted according to the specified position of the defect. However, there has been a problem that, in some cases, it is difficult to hide a phase defect in the region of an absorber pattern no matter how much the pattern layout is shifted. Thereby, in such a case, it becomes difficult to perform writing processing, and, simultaneously, difficult to fabricate an EUV exposure mask.
Accordingly, it becomes difficult to manufacture semiconductor devices which are fabricated by a pattern transferring or printing operation with an EUV exposure mask. Conventionally, no sufficient method for solving these problems has been established.